Semiconductor chips typically are connected to external circuitry through contacts on a surface of the chip. The contacts on the chip typically are disposed in the regular patterns such as a grid substantially covering the front surface of the chip, commonly referred to as an "area array" or in elongated rows extending parallel to and adjacent each edge of the chip front surface. Each contact on the chip must be connected to external circuitry, such as the circuitry of a supporting substrate or circuit panel. Various processes for making these interconnections use prefabricated arrays of leads or discrete wires. For example, in a wirebonding process, the chip is physically mounted on the substrate. A fine wire is fed through a bonding tool. The tool is brought into engagement with the contact on the chip so as to bond the wire to the contact. The tool is then moved to a connection point of the circuit on the substrate, so that a small piece of wire is dispensed and formed into a lead, and connected to the substrate. This process is repeated for every contact on the chip.
In the so-called tape automated bonding or "TAB" process, a dielectric supporting tape, such as a thin foil of polyimide is provided with a hole slightly larger than the chip. An array of metallic leads is provided on one surface of the dielectric film. These leads extend inwardly from around the hole towards the edges of the hole. Each lead has an innermost end projecting inwardly, beyond the edge of the hole. The innermost ends of the leads are arranged side by side at spacing corresponding to the spacings of the contacts on the chip. The dielectric film is juxtaposed with the chip so that hole is aligned with the chip and so that the innermost ends of the leads will extend over the front or contact bearing surface on the chip. The innermost ends of the leads are then bonded to the contacts of the chip, as by ultrasonic or thermocompression bonding. The outer ends of the leads are connected to external circuitry.
In a so-called "beam lead" process, the chip is provided with individual leads extending from contacts on the front surface of the chip outwardly beyond the edges of the chip. The chip is positioned on a substrate with the outermost ends of the individual leads protruding over contacts on the substrate. The leads are then engaged with the contacts and bonded thereto so as to connect the contacts on the chip with contacts on the substrate.
The rapid evolution of a semiconductor art in recent years has created a continued demand for progressively greater numbers of contacts and leads in a given amount of space. An individual chip may require hundreds or even thousands of contacts, all within the area of the chip front surface. For example, a complex semiconductor chip in current practice may have a row of contacts spaced apart from one another at center-to-center distances of 0.5 mm or less and, in some cases, 0.1 mm or less. These distances are expected to decrease progressively with continued progress in the art of semiconductor fabrication.
With such closely-spaced contacts, the leads connected to the chip contacts, such as the wires used in wirebonding leads in the tab process and beam leads must be extremely fine structures, typically less than 0.5 mm wide. Such fine structures are susceptible to damage and deformation. With closely spaced contacts, even minor deviation of a lead from its normal position will result in misalignment of the leads and contacts. Thus, a given lead may be out of alignment with the proper contact on the chip or substrate, or else it may be erroneously aligned with an adjacent contact. Either condition will yield a defective chip assembly. Errors of this nature materially reduce the yield of good devices and introduce defects into the product stream. These problems are particularly acute with those chips having relatively fine contact spacings and small distances between adjacent contacts.
Copending, commonly assigned U.S. patent application 07/919,772, filed Jul. 24, 1992 (the "772 application"), the disclosure of which is incorporated by reference herein, describes an improved system for connecting semiconductor chips to external circuitry. Certain embodiments of the invention set forth in the '772 application utilize a connection component having a support structure and electrically conductive leads. Each lead has a connection section extending across a gap in the support structure. The connection sections of the leads are flexible. Preferably, one end of each lead is detachably secured to the support structure, whereas the other end is permanently secured to the support structure and connected to a terminal mounted on the support structure. The connection component is positioned on a part of a semiconductor chip assembly, such as the chip itself, so that the leads overlie contacts on the part or chip. The connection sections of the leads are bonded to the contacts on the chip by engaging each connection section with a tool, forcing the tool downwardly to break the detachable end of the lead from the support structure and bring the connection section into engagement with a contact on the chip. The tool is used to apply heat and/or ultrasonic vibrations to the lead, thereby forming a bond between the lead and the contact of the chip. This process is repeated for each lead, until all the leads have been bonded to the contacts on the chip. After the connection component has been electrically connected to the contacts of the chip, the terminals of the connections component can be used to connect the chip to other, external circuitry as, for example, by bonding the terminals of the connection component to an external substrate such as a circuit panel.
In the preferred arrangements disclosed in the '772 application, the bonding tool is arranged to capture and align the lead. Thus, the bonding tool may be a blade-like device with an elongated bottom edge and with a groove extending lengthwise along such bottom edge for engaging leads to be bonded. The groove may have a central plane and surfaces sloping upwardly from the sides of the groove towards the central plane. When the tool is roughly aligned with a lead, so that the lengthwise axis of the bottom edge and groove are generally parallel to the lengthwise axis of the connection section of the lead, the groove will engage the lead and guide it into precise alignment with the tool. Thus, the tool can be aligned in sequence with each contact, and engaged with a lead. Even if the lead is slightly out of alignment with the contact and tool at the beginning of the operation, the tool will bring the lead into precise alignment with the tool and hence with the contact during the downward motion of the tool. Thus, minor dimensional variations in the connection component do not impede the process, even where the contacts are provided at very small spacings.
The preferred embodiments described in the '772 application are highly advantageous, but still further improvement would be desirable. In many cases, the connection sections of different leads extend in different, mutually orthogonal directions. For example, many common chips are generally rectangular and have contacts disposed in rows extending along the edges of the chip. The rows of contacts on adjacent edges extend in mutually orthogonal directions. The connection sections of the leads associated with each row of contacts on the chip must be arranged side by side, so that the connection sections of the leads extend orthogonally to the length of the row. Thus, where the rows of contacts extend in mutually orthogonal directions along different edges of the chip, the connection sections of the leads likewise extend in mutually orthogonal directions. Typically, the tool is positioned so that the lengthwise axis of the bottom edge extends parallel to the connection sections in one row, and the tool is then advanced stepwise down the row, bonding each of the leads in the row seriatim. When the row is completed, the chip and support structure must be rotated 90.degree. relative to the tool so as to properly align the tool for engagement with the connection sections of the next row.
The rotation step consumes appreciable time in production and requires that the apparatus be equipped with a precise, rotatable stage or mounting. Moreover, the rotation step can introduce additional misalignments between the connection sections and the tool. Accordingly, it would be desirable if tools and methods could be provided which incorporate the advantages of the preferred embodiments disclosed in the '772 application but which avoid the need for the rotation step and mechanism.